Form your pie crust into your pan, then place it in the freezer. If you are doing a lattice top as I showed in the post, make this as well.
In a small bowl, combine the ½ cup brown sugar, ½ cup granulated sugar, cinnamon, nutmeg, and cornstarch. Set aside.
Place apples, water, and butter into heavy bottom saucepan over medium heat. Cook for about 5 minutes, stirring occasionally, but being careful not to break up the apples. Now, add in the bowl of dry ingredients. Mix well. Continue to cook, stirring constantly for another 3 minutes. Remove from heat and allow to cool to room temp.
Once it is cool, add the blueberries and mix gently.
Preheat oven to 375 degrees.
Pour the filling into the pie shell. Fill with the cooled apple pie filling. Top with the lattice pie topping.
Mix your egg and 2 tablespoons of milk together in a small bowl and mix well. This is the egg wash. Brush the top with the egg wash and sprinkle with sugar.
Place in oven and bake for 15 minutes. Reduce heat to 350 degrees and continue baking another 30-45 minutes. I check with the color of the crust. You want a golden brown. A good way to check is by inserting a skewer into the apples. You want them to be tender, but still hold their shape. It will keep cooking once the pie is removed, so you don't want them too soft when you remove them from the oven.
You can serve it immediately, or you can wait until it cools slightly. Chilling it overnight is also a good option. If I am being totally honest, I love apple pie for breakfast! The photos in the post are of the pie after it has been chilled overnight.